Film for applying compressive stress to ceramic materials
A method to provide compressive stress to substrates includes depositing a film on a ceramic substrate at a deposition temperature (Td) to form an article, the film having a difference relative to the ceramic substrate at Td in a coefficient thermal expansion (CTE) of at least 1.0×10 −6 /K and a difference in a refractive index >0.10. At least a portion of the thickness the film is converted in at least one of composition, phase and microstructure by lowering or raising the temperature from Td to reach a changed temperature (Tc) that is at least 100° C. different from Td. The film converting conditions result in the converted film portion providing a difference in refractive index at the Tc between the converted film and the ceramic substrate of ≤|0.10|. The temperature of the article is then lowered to room temperature.
1. A method to provide compressive stress to substrates, comprising:
depositing a nitride film on a ceramic substrate at a deposition temperature (Td) to form an article, said nitride film having a difference in a coefficient thermal expansion (CTE) relative to said ceramic substrate at said Td of at least 1.0×10−6/K and a difference in a refractive index of greater than (>) 0.10;
converting said nitride film comprising lowering or raising a temperature from said Td to reach a changed temperature (Tc) that is at least 100° C. different from said Td, wherein conditions for said converting result in said nitride film becoming in at least a portion of its thickness a converted film through a composition change such that there is an increase in oxygen content by at least (≥) 10 mole percent, a decrease in nitrogen content by at least (≥) 10 mole percent, or a decrease in carbon content by at least (≥) 10 mole percent, so that a difference in said refractive index at said Tc of said converted film and said ceramic substrate is ≤|0.10|, and
lowering a temperature of said article from said Tc to room temperature, wherein said nitride film is an AlO a N b film, wherein a+b<1.5, a SiCON film, or a SiAlCON film.
2. The method of claim 1 , wherein said substrate comprises sapphire.
3. The method of claim 1 , wherein said converting comprises flowing one or more of carbon, oxygen or nitrogen containing gases.
4. The method of claim 1 , wherein said article is optically transparent.
5. The method of claim 1 , wherein said substrate comprises a silica-based glass, sapphire, alumina, or a spinel.
6. The method of claim 1 , wherein said portion of said converted film is under a compressive stress, and wherein said substrate is under a tensile stress.
7. The method of claim 1 , wherein said article comprises a display screen of a cellular phone.
8. The method of claim 1 , wherein said portion of said converted film is from 10% to 80%.
9. The method of claim 1 , wherein after said converting said difference in said refractive index of said nitride film and said ceramic substrate is <10.051.
10. The method of claim 1 , wherein, after said converting of said nitride film, a compressive stress in said film is 1 MPa to 10 GPa.
11. The method of claim 1 , wherein said nitride film is an AlO a N b film, wherein a+b<1.5 and wherein said converted film is an AlO x N y film wherein x+y<1.5 and wherein x>a and y<b.
12. The method of claim 11 , wherein a is from 0 to 0.5.
13. The method of claim 11 , wherein a=0.
14. The method of claim 11 , wherein x is from 0.5 to 1.5.
15. The method of claim 11 , wherein x=1.5 and y=0.
16. The method of claim 1 , wherein said nitride film is a SiCON film and wherein said converted film is SiO x N y film, wherein x+y<2.